2.7.33 Function Properties

Condition: Determine the display \ [f: \ mathbb {r} {2} \ rightarrow \ mathbb {r}, \ quad f (x, y) = \ frac {x^{2}-| y |} {x^{2}+y^{2} \] when \ ((x, y) \ neq (0.0) \) and for \ (f (0.0) = 0 \). At what points is the function differentiated?